If you can still access the site, just without any styles or some broken part maybe it could be just the path is not updated yet to your development environment. Drupal store the path to your theme, modules etc in cache so on production server the path could be /var/www/yoursite or something but on development machine the path is /home/yourname/yousite.
If that the case, just login as admin (use /user or q=user to get the login page) and then go the admin/build/modules and admin/build/themes. That would refresh the cache with the new path.